1. Field of the Invention
The present invention relates generally to an electronic apparatus for measuring the thickness of a wide variety of materials and products, and more particularly, to a hand-held, high sensitivity digital ultrasonic thickness gage primarily for measuring the wall thickness of objects such as heat exchanger tubing, pressure vessels, storage tanks, ship hulls, piping and valves, plates, slabs, etc. While mostly used for gaging metals, the gage is also applicable to glass, plastic, fiberglass and other materials which satisfactorily conduct ultrasonic waves.
2. Prior Art
Portable hand-held digital thickness gages are already in the prior art. By way of example, a Model DM2 Meter is sold by Krautkramer-Branson of Stratford, Conn. However, each such prior art portable hand-held thickness gage suffers from one or more disadvantages which the present invention is designed to overcome. More specifically, the principal advantage of all such gages is the convenience of use which a portable hand-held battery operated digital thickness gage can provide those in the field whose job it is to inspect heat exchanger tubing, pressure vessels, storage tanks, ship hulls, piping and valves as well as similar objects to determine whether or not the thickness of such devices is either satisfactory or which will require rejection, repair or replacement. Typically, in order to provide a thorough and complete inspection of such devices it is often necessary to make a large number of measurements in the period of one 8-hour working day. Accordingly, a device that may be hand-held and battery operated with only a minimum of convenient calibration adjustments, minimizes the difficulty, time consumption and therefore the labor costs related to carrying out such a large number of measurements.
Unfortunately, the prior art hand-held digital ultrasonic thickness gages that are currently available significantly diminish the outerwise advantageous nature of such measurement devices by requiring the user to make certain inconvenient pretest adjustments such as zero calibration and material velocity adjustments which require the use of either a screw driver or thumbwheel switches which are relatively inconvenient to operate. In addition to the general inconvenience disadvantage of pretest adjustments that are necessary in such prior art devices, the very control mechanism for making these adjustments is also highly disadvantageous. More specifically, these adjustments render it more likely that the operator will inadvertently touch a thumbwheel switch or a screwdriver adjustment without realizing it, thereby uncalibrating the instrument and rendering the measurement erroneous. Furthermore, these controls provide paths into the interior of the instrument for moisture and other elements which can be particularly disadvantageous during outdoor work or work in high humidity indoor environments. As a result, the likelihood of failure of the instrument and the expense of inspection "downtime", need for costly repairs or replacement of the instrument, or its components, becomes more probable, thereby decreasing the otherwise advantageous nature of the portable hand-held digital thickness gage.